1. Field of the Invention
The present invention relates to a printed circuit board and its heat dissipating metal surface layout, and more particularly to a printed circuit board that goes through a soldering furnace to form a protruding solder at a bare copper position on the printed circuit board, so as to increase the heat dissipating area.
2. Description of Prior Art
To enhance the heat dissipating effect of a printed circuit board (PCB), most of the printed circuit boards add heat dissipating holes, electroplate metal films, install metal lumps on the backside of the printed circuit boards, or directly coat a heat dissipating paste onto the printed circuit boards for dissipating heat.
Referring to FIGS. 1 and 2 for a printed circuit board 1a that uses a copper foil for dissipating heat, the printed circuit board 1a comprises an insulating substrate 10a, a layer of copper foil 11a plated onto the substrate 10a for dissipating heat, and an insulating coating 12a coated onto the surface of the copper foil 11a. To maximize the heat dissipating effect of a limited area of the copper foil 11a, a portion of the insulating coating 120a is usually removed, so that the originally covered copper foil 11a is exposed to the outside to form a bare copper portion 110a, and the solder 13a is attached onto the bare copper portion 110a by a soldering furnace, such that the strong cohesion of the solder aggregates a certain amount of solder to form a protruding thickness, so as to increase the exposed surface area for dissipating heat.
Referring to FIG. 3 together, the removal of the insulating coating 120a is usually done by using a slender shape and a layout with intervals arranged in a single direction. Although such arrangement can avoid an excessively large area of a bare copper portion 110a and provide an even protrusion of the solder 13a, yet the cohesion and adhesion along the lengthwise direction are still uneven thus causing a larger thickness at the middle and a smaller thickness on both sides. Such phenomenon is caused by the uneven adhesion between the center and both sides and the uneven cohesion of the solder when the liquid solder is attached onto the copper foil, and thus more solders 13a are aggregated towards the center, and insufficient solders are provided for the natural formation of the protrusion on both sides. The relative surface area is smaller, and the cross-sectional shape of the solder 13a along the lengthwise direction is inconsistent, which adversely affects the transmission of current.
In view of the description above, the inventor of the present invention designed a feasible solution to effectively overcome the foregoing shortcomings.